Structural investigations of human serum albumin, transferrin, the B-chain of haptoglobin, the group-specific protein and ceruloplasmin are being conducted in order to detect amino acid alterations or sequence rearrangements in inherited variants of these molecules. Subunit characterization in the serum proteins will provide evidence for the number of structural genes controlling the conformation of each protein. Computer analyses ultimately will be utilized to detect and evaluate relationships among proteins, which we have studied, in addition to sequences performed in other laboratories, that are too remote to be recognized visibly by their unchanged amino acids. When enough sequence information is available the phylogenetic tree of families of proteins can be constructed.